Overview Kexec & Kdump

Kexec is a fastboot mechanism which allows booting a Linux kernel from the context of already running kernel without going through BIOS. BIOS can be very time consuming especially on the big servers with lots of peripherals. This can save a lot of time for developers who end up booting a machine numerous times.

Kdump is a new kernel crash dumping mechanism and is very reliable because the crash dump is captured from the context of a freshly booted kernel and not from the context of the crashed kernel. Kdump uses kexec to boot into
a second kernel whenever system crashes. This second kernel, often called a capture kernel, boots with very little memory and captures the dump image.

The first kernel reserves a section of memory that the second kernel uses to boot. Kexec enables booting the capture kernel without going through BIOS hence contents of first kernel’s memory are preserved, which is essentially
the kernel crash dump.

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